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COPPER SULPHATE                                   63


See Bleaching Powder


CHC13 = 119-38

Colourless heavy liquid of peculiar odour, D = 1-490-1-493, 61-
62°, very slightly soluble in water, miscible with alcohol. The impurities
to be looked for are especially chlorine, hydrochloric acid, chloro-compounds
(of ethylidene and amyl) and aldehydes, the tests being carried out as
follows :

1.  Volatility.—20—30 c.c.,  evaporated spontaneously or at a gentle
heat, should leave no appreciable residue of unpleasant, irritating odour
(phosgene, amyl or -valeric compounds}.

2.  Reaction, Hydrochloric Acid.—To 5 c.c. are added i drop of a
saturated solution of Congo red in absolute alcohol :  if the chloroform has
undergone change, a blue coloration appears.

5 c.c. are shaken with 2-5 c.c. of water, which should not become acid
or give a 'turbidity with silver nitrate (hydrochloric acid).

3.  Other Tests.—5 c.c.,  shaken with potassium iodide solution or
with iodide-starch paste, should give no red or blue coloration (chlorine).

20 c.c., shaken with 12 c.c. of pure cone, sulphuric acid, should give no
brownish-yellow coloration, even after 24 hours (chlorinated ethylidene or
amyl compounds).

A fragment of caustic potash, added to 5 c.c. of the sample, should
remain white and the liquid should not turn yellow in 12 hours.

Pure chloroform for medical purposes should answer all the above tests.
It is permissible to add 0-5-1% of alcohol as a preservative. •


CuS04 + 5H20 = 249-57

Blue crystals which effloresce somewhat in the air, soluble in 3-5 parts
of cold water. It is sold fairly pure, only containing, as a rule, small quan-
tities of ferrous sulphate and rarely zinc, magnesium and calcium sulphates
or free sulphuric acid. Its value depends on the proportion of pure crys-
tallised copper sulphate and its analysis includes mainly determinations
of the copper and water (3 and 4). In some cases determinations of the
iron and free sulphuric acid may be required.

1.  Iron.—4 grams are dissolved in 20 c.c. of water, an excess of ammonia
added, the liquid filtered and the filter washed until it is no longer blue ;
in presence of iron, a brownish deposit or spot remains on the filter.

2.  Zinc, Magnesium,  Calcium and other Metals.—2 grams are
dissolved in 40 c.c. of water, the solution being acidified with hydrochloric
acid and the copper precipitated with hydrogen sulphide;   the filtered
liquid, evaporated and ignited, should leave no appreciable residue.    Ifor yellow precipitate (potas-